Quantum interference spectroscopy in the vacuum ultraviolet

With two experiments on respectively krypton at 2 × 212 nm and xenon at 125 nm we have demonstrated the method of quantum interference spectroscopy in the deep- and vacuum-ultraviolet. Multiple pulses from a frequency comb laser are amplified and frequency converted and used in a Ramsey-like direct excitation scheme. In the Kr experiment we achieved a 150 kHz accuracy for isotope shift values and a 3.5 MHz accuracy for the absolute transition frequency. With the Xe experiment we demonstrated that the same method can be used in combination with frequency upconversion in a gas without significant distortion of the phase coherence, therefore allowing sub-MHz resolution spectroscopy at VUV and XUV wavelengths.